ABSTRACT Title of Thesis: ICHTHYOPLANKTON COMMUNITY STRUCTURE AND FEEDING ECOLOGY IN THE PATUXENT RIVER ESTUARINE TRANSITION ZONE Patrick Anthony Campfield, Master of Science, 2004 Thesis directed by: Professor Edward D. Houde Marine Estuarine and Environmental Sciences Program Surveys were conducted during spring-early summer of 2000 and 2001 to investigate the spatiotemporal structure of ichthyoplankton assemblages, including hatchery-released American shad Alosa sapidissima, and feeding of larval fishes in the Patuxent River, Chesapeake Bay. Ichthyoplankton, zooplankton, and hydrographic data were collected across the Patuxent’s estuarine transition zone, including the salt front and Estuarine Turbidity Maximum region. Recaptured American shad larvae cohort mortality (M = 0.20 to 3.01•d-1) and growth (G = -1.28 to 0.87 mm•d-1), low dispersal (±0.4km•d-1), and feeding habits similar to co-occurring species, suggest that the best production will result from larval shad releases upriver of the salt front in early to mid- May. Two ichthyoplankton assemblages were distinguished: 1) riverine – characterized by anadromous species and 2) estuarine – characterized by naked goby Gobiosoma bosc. Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and the larval prey Bosmina longirostris (Cladocera) concentrations were indicators of larval abundance. Abundance, taxonomic diversity, and dietary overlap and potential for competition among larval taxa were highest within and up-estuary of the salt front of the estuarine transition zone. ICHTHYOPLANKTON COMMUNITY STRUCTURE AND FEEDING ECOLOGY IN THE PATUXENT RIVER ESTUARINE TRANSITION ZONE by Patrick Anthony Campfield Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Master of Science 2004 Advisory Committee: Professor Edward D. Houde, Chair Professor Walter R. Boynton Associate Professor Thomas J. Miller ©Copyright by Patrick Anthony Campfield 2004 ACKNOWLEDGEMENTS Several organizations and many individuals contributed to support of this study. I thank Maryland Sea Grant for supporting the research (NOAA Award No. NA16RG2207, Maryland Sea Grant R/F-90), S. Minkkinen and B. Richardson of the Maryland Department of Natural Resources Anadromous Fish Restoration Group for collaborating and providing hatchery-produced American shad larvae, and the University of Wisconsin Biological and Biomaterials Preparation, Imaging, and Characterization Laboratory for assisting with epifluorescent microscopy analysis. I am grateful to the American Fisheries Society Marine Fisheries Section, the Chesapeake Biological Laboratory Graduate Education Committee, and the University of Maryland Graduate School for provision of travel funds to present research results at scientific meetings. Many individuals at the Chesapeake Biological Laboratory provided support in various forms, including B. Pearson, J. Bichy, D. Craige, J. Boynton, E. North, J. Shoji, W. Morrison, E. Martino, and others who assisted in the field and provided advice on statistical analyses. Special thanks to S. Gibson for assisting with processing of zooplankton samples, and J. Olney and D. Bilkovic at the Virginia Institute of Marine Sciences for assisting with larval fish identifications. Thanks to B. Cornwall and other members of the UMCES Research Fleet for advice on sampling and capable assistance in surveys aboard the RV Pisces, RV Orion, and RV Aquarius. I am grateful to E. Houde for the opportunities and professional support he has provided. Thanks also to my other committee members, W. Boynton and T. Miller, for ii their valuable advice and instruction. Thanks to my wife and other family members for their continued support, patience, and perspectives. iii TABLE OF CONTENTS List of Tables………………………………………………………………………….......v List of Figures……………………………………………………………………………vii Chapter One: Evaluating stocking protocols for American shad larvae......……… Abstract……………………………………………………………………………1 Introduction……………………………………………………………………......3 Methods……………………………………………………………………………6 Results……………………………………………………………………………15 Discussion………………………………………………………………………..22 Tables …………………………………………………………………………....29 Figures …………………………………………………………………………...34 Literature Cited…………………………………………………………………..49 Chapter Two: Ichthyoplankton assemblages in the Patuxent River estuarine transition zone……………………………………………………… Abstract…………………………………………………………………………..55 Introduction……………………………………………………………………....56 Methods…………………………………………………………………………..57 Results……………………………………………………………………………62 Discussion………………………………………………………………………..72 Tables………...…………………….…………………………………………….84 Figures……………………………………………………………………………90 Literature Cited...……………………………………………………………….103 Chapter Three: Feeding ecology of larval fishes in the Patuxent River estuarine transition zone..................................................…………………….. Abstract…………………………………………………………………………112 Introduction……………………………………………………………………..114 Methods…………………………………………………………………………116 Results…………………………………………………………………………..122 Discussion………………………………………………………………………132 Tables …………………………………………………………………………..143 Figures ………………………………………………………….………………146 Literature Cited……….………………………………………………………...160 Chapter Four: Summary and Conclusions..........................................................167 iv TABLES 1.1. Patuxent River hydrographic conditions and larval shad numbers and ages at each stocking event in 2000 and 2001. Hatchery water temperatures are included for comparison. River flow data are from a U.S. Geological Survey gauge at rk130. 1.2. Percent survival of American shad larvae in 24-hr laboratory experiments (on dates of stocking) to evaluate survival potential of stocked larvae. Patuxent River water was taken from the site of each respective stocking event. Experiments were conducted in 76- liter aquaria at the Chesapeake Biological Laboratory. 1.3. Numbers of American shad larvae recaptured in the Patuxent River from stocked cohorts in 2000 and 2001. 1.4. American shad larvae, Patuxent River. (a) Prey preferences of larval shad by cohort; * indicates significant (p < 0.05) Strauss index L values; (b) Dietary overlap in larval shad cohorts; * indicates significant (p < 0.05) Czechanowski index O values. 1.5. Patuxent River larval fish feeding analyses. Prey preferences, Strauss index L values (a) and dietary overlap, Czechanowski index O values (b) in larval fish taxa and size classes common in the freshwater nursery area of the Patuxent River. * indicates significant (p < 0.05) values. 2.1. Spawning temperatures for anadromous and estuarine fishes in Chesapeake Bay (Funderburk et al. 1991). 2.2. Survey descriptions (a) and sampling station locations (b) for Patuxent River ichthyoplankton surveys in 2000 and 2001. 2.3. Year 2000. Larval fish species composition, frequency of occurrence (Freq = proportion of tows positive), CPUE (no.•tow-1), and SE of CPUE by region in the Patuxent River estuarine transition zone in spring-early summer 2000. The ‘Salt front’ region includes stations ±3-km from the salt front location (see Fig. 1.4). H’ = Shannon- Wiener diversity index values (H’max = 2.0). v 2.4. Year 2001. Larval fish species composition, frequency of occurrence (Freq = proportion of tows positive), CPUE (no.•tow-1), and SE of CPUE by region in the Patuxent River estuarine transition zone in spring-early summer 2001. The ‘Salt front’ region includes stations ±3-km from the salt front location (see Fig. 1.4). H’ = Shannon- Wiener diversity index values (H’max = 2.0). 2.5. Multiple regression models evaluating relationships between concentrations (no.•m-3) of common larval taxa (alewife, striped bass, white perch, and naked goby) and abiotic and biotic factors in 2000 and 2001. Organism concentrations were log10(x+1)- transformed. Independent variables were entered into models using stepwise procedures. Parameter estimates and standard errors (in parentheses) are reported for independent variables that described a significant amount of variability in larval concentrations (* = p < 0.10, ** = p < 0.05, *** = p < 0.01). Akaike’s Information Criteria (AIC) indicate quality of model fit. The salt front location was modeled as a dichotomous variable (0 when station located at or up-estuary of the salt front, 1 when below). N2000 = 11; N2001 = 14. 2.6. Cohort-specific growth rate estimates (mm•d-1) based on length-frequency analyses for larval alewife, striped bass, white perch, and naked goby in 2000 and 2001. Cohorts listed chronologically. 3.1. Freshwater Region. (a) Prey preferences and importance of prey types and (b) dietary overlap in larval fish taxa and size classes common in the freshwater region of the Patuxent River, 2000-2001. Relative importance index Ria values in italics. * indicates significant (p < 0.05) Strauss selection index L values. Significance of Czechanowski overlap index O values indicated by * = p < 0.05 or ** = p < 0.01. 3.2. Salt Front Region. (a) Prey preferences and importance of prey types and (b) dietary overlap in larval fish taxa and size classes common in the salt front region of the Patuxent River, 2000-2001. Relative importance index Ria values in italics. * indicates significant (p < 0.05) Strauss selection index L values. Significance of Czechanowski overlap index O values indicated by * = p < 0.05 or ** = p < 0.01. 3.3. Oligohaline Region. (a) Prey preferences and importance of prey types and (b) dietary overlap in larval fish taxa and size classes